SOS_Mutex

Ewald Cress continues his dive into system internals, this time looking at SOS_Mutex:

Put differently, we can build a mutex from an auto-reset EventInternal by tacking on an owner attribute, making a rule that only the owner has the right to signal the event, and adding assignment of ownership as a fringe benefit of a successful wait. A nonsignalled event means an acquired mutex, and a signalled event means that the next acquisition attempt will succeed without waiting, since nobody currently owns the mutex. The end result is that our SOS_Mutex class exposes the underlying event’sSignal() method and its own take on Wait(). From the viewpoint of the mutex consumer, the result of a successful wait is that it owns the mutex, and it should act honourably by calling Signal() as soon as it is done using the resource that the mutex stands guard over.

There’s some deep detail here, so this is definitely one of those “after your first cup of coffee” posts to read.

Related Posts

Looking At Compressed Pages

Jess Pomfret shows us what compressed data looks like in SQL Server: We first need to switch on trace flag 3604: this will write the output of our DBCC PAGE command to the messages tab instead of the event log. There are 4 parameters for DBCC PAGE: we will need to pass in the database name (or id), the […]

Read More

When A Procedure Has Multiple Plan Cache Entries

Arthur Daniels shows that multi-statement stored procedures can have multiple entries in the plan cache: So we have two entries for this stored procedure. I included the statement sql handle to show that each statement handle has its own text. Let’s parse that text to see each statement. I copied the parsing SQL from this Plan […]

Read More

Categories

June 2016
MTWTFSS
« May Jul »
 12345
6789101112
13141516171819
20212223242526
27282930